Mode-locking of incommensurate phase by quantum zero point energy in the Frenkel-Kontorova model

In this paper, it is shown that a configuration modulated system described by the Frenkel-Kontorova model can be locked at an incommensurate phase when the quantum zero point energy is taken into account. It is also found that the specific heat for an incommensurate phase shows different parameter-dependence in sliding phase and pinning phase. These findings provide a possible way for experimentalists to verify the phase transition by breaking of analyticity.Comment: 6 pages in Europhys style, 3 eps figure

Constraining Factors in Hungarian Carp Farming: An Econometric Perspective

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Thermal effects on atomic friction

We model friction acting on the tip of an atomic force microscope as it is dragged across a surface at non-zero temperatures. We find that stick-slip motion occurs and that the average frictional force follows $|\ln v|^{2/3}$, where $v$ is the tip velocity. This compares well to recent experimental work (Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all microscopic parameters. We calculate the scaled form of the average frictional force's dependence on both temperature and tip speed as well as the form of the friction-force distribution function.Comment: Accepted for publication, Physical Review Letter

Quantum Frenkel-Kontorova Model

This paper gives a review of our recent work on the quantum Frenkel-Kontorova model. Using the squeezed state theory and the quantum Monte Carlo method, we have studied the effects of quantum fluctuations on the Aubry transition and the behavior of the ground state wave function. We found that quantum fluctuations renormalize the sinusoidal standard map to a sawtooth map. Although quantum fluctuations have smeared the Aubry transition, the remnants of this transition are still discernible. The ground state wave function also changes from an extended state to a localized state. The squeezed state results agree very well with those from the Monte Carlo and mean field studies.Comment: 20 pages in elsart.sty, 11 eps figure

A simple variational approach to the quantum Frenkel-Kontorova model

We present a simple and complete variational approach to the one-dimensional quantum Frenkel-Kontorova model. Dirac's time-dependent variational principle is adopted together with a Hatree-type many-body trial wavefunction for the atoms. The single-particle state is assumed to have the Jackiw-Kerman form. We obtain an effective classical Hamiltonian for the system which is simple enough for a complete numerical solution for the static ground state of the model. Numerical results show that our simple approach captures the essence of the quantum effects first observed in quantum Monte Carlo studies.Comment: 12 pages, 2 figure

Atomic scale friction between clean graphite surfaces

We investigate atomic scale friction between clean graphite surfaces by using molecular dynamics. The simulation reproduces atomic scale stick-slip motion and low frictional coefficient, both of which are observed in experiments using frictional force microscope. It is made clear that the microscopic origin of low frictional coefficients of graphite lies on the honeycomb structure in each layer, not only on the weak interlayer interaction as believed so far.Comment: 4 pages, 7 figure

Defect-induced perturbations of atomic monolayers on solid surfaces

We study long-range morphological changes in atomic monolayers on solid substrates induced by different types of defects; e.g., by monoatomic steps in the surface, or by the tip of an atomic force microscope (AFM), placed at some distance above the substrate. Representing the monolayer in terms of a suitably extended Frenkel-Kontorova-type model, we calculate the defect-induced density profiles for several possible geometries. In case of an AFM tip, we also determine the extra force exerted on the tip due to the tip-induced de-homogenization of the monolayer.Comment: 4 pages, 2 figure

A Kárpát-medencei paleogén szerkezetalakulás rekonstrukciója a magmás tevékenység és üledékképződés egyidejű jellemzésével = The reconstruction paleogene structural evolution of the Carpathian basin using parallel evaluation of sedimentary and volcanic processes

Megtaláltuk, leírtuk és megmintáztuk a Rm 7, 28, 63, 79, 87, 109, 117 és 118 jelű fúrásokat, melyekben andezit közé települve üledékes kőzetek találhatók. Őslénytani és kőzettani vizsgálataink nyomán összefoglaló megállapításunk az hogy a magmás működés több szakaszú, kezdete a felső eocénre tehető (a Szépvölgyi Mészkő Formáció), és zárótagjai az késő oligocénben keletkeztek (31 M év). A magmás múködés korai szakaszát követte jelentős hidrotermális elváltozás és szinesfém ércesedés, a zárótagok kialakulását követően jöttek létre a felszínközeli nemesfém (Au, Ag) dúsulások. Ellenőriztük, illetve a recski mélyszinti adatbázissal összekapcsoltuk a recski lahócai aranyérc kutatások során kapott geokémiai adatokat. Arecski érces ásványvagyon értékét jelentősen növeli az arany dúsulások mértékének a kutatásaink során elvégzett helyesbítése. A korábbi 0,1mg/kg átlagos Au koncentráció helyett a mélyszinti dioritok 0,3 mg/kg, a szkarnos rézércek 1 mg/kg feletti Au koncentráció értékeket mutattak. A képződmények gazdaságföldtani potenciálját jelentősen megnöveli hogy a paleogén magmás működés a korábban véltnél fiatalabb, az ezt követő arany ércesedés kialakulása a felső oligocénbe esik. Ez a hidrotermális működési szakasz érinthette az idősebb oligocén képződményeket, s ezekben Au ércesedés kutatása indokolttá vált. A recski és az ország egyéb területeiről ismert paleogén vulkanitok egységes szerkezeti értelmezést nyertek, s ismert koradataik összhangja is megteremtődött. | We have checked and re-logged several drillcores, like Recsk Rm 7, 28, 63, 79, 87, 109, 117, 118. According to our paleontological and petrographical data we assume that the igneous activity was of multi-stage character. It started in the Upper Eocene (Szepvolgyi Limestone Formation) and finished in the Late Oligocene Egerian stage (31 M yrs radiometric age) The early magmatic activity was followed by significant hydrothermal alteration ans base metal mineralization. The Au-Ag enrichments postdated the latest volcanic emplacements. We checked and linked to the Recsk Deeps database the geochemical data obtained from the Lahóca gold explorations. The value of the Recsk ore resource has been increased by the corrections which have been carried out in the average gold content estimations - 0,3 mg/kg instead of the previously suggested 0,1 mg/kg in the porphyry Cu ores, and over 1 mg/kg in the skarn Cu ores. The discovered younger geological age of the ore formation has important economic implication since it sets the age of the Au mineralization into the Late Oligocene, thus providing economic potential for gold enrichment in the earlier Oligocene sediments. Our investigations has resulted a better understanding of the age relationships of the igneous rocks at Recsk and in other regions of the country